In the present invention, a term “wire” denotes not only a wire itself but also a cable.
In order to develop an antenna for a portable phone for receiving data of mobile communication and digital multimedia broadcasting (DMB), various antenna technologies have been introduced such as technologies for high efficiency, low loss, omni-directional radiation pattern, impedance matching for improving a radiation efficiency, a broad bandwidth characteristic, a low power consumption, for reducing the size and width of the antenna, and for simplifying a design, for protecting human from harmful radiated electromagnetic waves, for an electromagnetic environment and for improving portability.
Among technologies, the technology for making the antenna smaller and light-weighted is a technology for improving the portability and has been receiving attention in an antenna field for a mobile communication terminal such as a cellular phone, a personal communication station (PCS) phone and a global system for mobile communication (GSM) phone and a DMB phone for receiving data of digital multimedia broadcasting (DMB).
Especially, an antenna for receiving data of digital multimedia broadcasting (DMB) is generally very large. For example, a length of an antenna for Korea DMB data which is broadcasted at 200 MHz band is about 37 cm. Therefore, the large antenna makes a user inconvenient to carry with a portable phone putted in a pocket and makes the appearance of the portable phone detracted. Furthermore, the large antenna makes a manufacturing process thereof complicated. Therefore, demands of a small monopole antenna have increased.
As conventional antennas for a portable phone, a whip antenna, a helical antenna, a slave antenna, an inverted-F antenna, a planar inverted-F antenna, a diversity antenna, a microstrip antenna, a chip antenna, a twisted loop antenna, a EID antenna, a N-type antenna were introduced. They may be classified into a monopole antenna group and other groups according to a method of exciting an electromagnetic field.
The monopole antenna denotes an antenna having a sufficient size of a ground plane and using image effects of the opposite side of the ground plane. The monopole antenna generally has an external structure to have a length of ¼ wavelength as like as a whip antenna, a helical antenna, a slave antenna and an N-type antenna. In order to reduce the size of the monopole antenna, a disk shaped top load is added at the end of the antenna, the monopole antenna is twisted as a meander type, or the monopole antenna is twisted as like as a helical antenna. However, there is a limitation to reduce the size of the monopole antenna smaller than a 1/10 wavelength through the conventional technologies.
On the contrary, an inverted-F antenna, a planar inverted-F antenna, a diversity antenna, a microstrip antenna, an EID antenna, a full short circuit planar inverted F antenna (FS-PIFA) and a radiation coupled dual-L antenna were introduced as other types of antennas for a portable phone. The planar inverted-F antenna, the microstrip patch antenna, a dielectric antenna are manufactured as a small internal antenna. In order to reduce the size thereof while lengthening the electric length thereof, a dielectric may be used or the antenna is bended or deformed to have a predetermined shape. However, it is very difficult to reduce a size of an antenna smaller than a 1/10 wavelength. It is also difficult to maintain an omni-directional radiation pattern of a vertical polarized wave because such antennas are disposed in a portable phone vertically coupled to a printed circuit board (PCB).
Furthermore, a method of manufacturing a small internal antenna having a long electric length by disposing a dielectric block inside a main body of a portable phone and using more than two sides of the dielectric block was introduced in a Korea Patent Application No. 10-2003-0032258. However, the method introduced in Korean Patent Application No. 10-2003-0032258 also has the same problems described above.
Recently, a small monopole antenna having a size smaller than a 1/10 wavelength was introduced. In order to reduce the size of the antenna, an inductance element such as a helical antenna is added at a disk monopole antenna. Although such a monopole antenna maintains broadband characteristics, the monopole antenna has a complicated structure and it is difficult to dispose the monopole antenna in a limited space such as an inside space of a portable phone. Furthermore, a conventional technology of miniaturizing an antenna by adding a gap capacitor at a feeder of a loop antenna was introduced. However, the conventional antenna has a narrowband characteristic and has difficulty to maintain an omni-directional radiation pattern which is commonly required for various types of portable phones.